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Powering 900 LED's from a cumputer power supply unit (PSU)?

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bubblebudman

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Hi guys!

This may be a silly question, but is it possible to supply enough of power from a computer power supply unit (PSU) for around 900 LED's?

Thank you in advance!
 

tcmtech

Banned
Most Helpful Member
assuming the standard LED takes about .1 watts then 900 of them would take 90 watts. But factor in resisters and other factors you would need to double that but still at 180 watts it could be done.

Why and what for?
There are more efficient ways of line powering that many LED's.
 

solis365

New Member
assuming the standard LED takes about .1 watts then 900 of them would take 90 watts. But factor in resisters and other factors you would need to double that but still at 180 watts it could be done.

Why and what for?
There are more efficient ways of line powering that many LED's.
Well he could just figure out the on resistance of the diodes and stack as many of them as necessary on each voltage rail to get the desired current.

i.e. 12V rail, at 1.7V forward drop just stack 6-7 LEDs up and youve got about 10-12V taken up by the LEDs. Then you only need to drop a small amount of voltage... hence a small resistor to get your 20mA. Less power dissipated.

I mean you could multiplex them and drive with a PWM source for high efficiency if you're just making a matrix of LEDs to display images, then you can just use persistence of vision. However if you actually need the full brightness of 900 LEDs, then whether you have 900 on at full for 100% of the time or 1800 on at full for 50% of the time youll get the same light output.

whats your application?




in short, most computer power supplies from this decade will output way more than 90W, you just have to be careful of where you put the LEDs (different voltage rails on computer PSUs have different max output power... i.e. 5V rail at 30A but 12V rail will only do 20A, for example.) And make sure you are within your supply's ratings - the number on the box might be different from what you end up drawing continuously, as theres peak and average power to deal with.

ask if you need more help!
 
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